Head mounted display

ABSTRACT

There is provided a head mounted display including a glasses-type frame to be worn on a head of an observer; two optical modules including two image creation devices, and two light guides having two light guide plates coupled one-to-one with the two image creation devices and placed closer to a center of a face of the observer than the image creation devices are as a whole, that guide light beams output from the image creation devices and output the light beams toward pupils of the observer; and an optical plate supporting the two light guides, wherein the optical plate is attached to a center part of the frame.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a head mounted display that is worn onthe head of an observer and displays images (virtual images).

2. Description of the Related Art

A virtual image display device (image display device) that allows a userto observe a two-dimensional image formed by an image creation device asa magnified virtual image by a virtual image optical system is proposedtoday (cf. e.g. Japanese Unexamined Patent Application Publication No.2006-162767).

Further, in order for an observer to observe a two-dimensional imageformed by an image creation device as a magnified virtual image by avirtual image optical system, a head mounted image display device usinga holographic diffraction grating is also proposed (cf. e.g. JapaneseUnexamined Patent Application Publication No. 2007-94175).

FIG. 14 shows a state where an observer is wearing a glasses-type imagedisplay device 90. At the left is a front view, and at the right is aplan view. The image display device 90 includes left and right imagecreation devices 1100L and 1100R that display images, and left and rightlight guides (optical devices) 1200L and 1200R that receive lightdisplayed on the image creation devices 1100L and 1100R and guide thelight to pupils 41L and 41R of the observer. The image display device 90composed of the image creation devices 1100L and 1100R and the lightguides 1200L and 1200R is attached to a glasses-type frame 1010. Theobserver fits temples 1015 extending from the ends of the frame 1010 torest on both ears, thereby wearing the image display device 90 on thehead of the observer.

SUMMARY OF THE INVENTION

However, when the observer wears the image display device 90, thetemples 1015 flex outward in the direction of the arrow A and,accordingly, a front part 1010 a of the frame 1010 is deformed in thedirection of the arrow B as shown at the right of FIG. 14. When such aphenomenon occurs, a changes occurs in the spatial position of an image(virtual image) created by light beams output from the light guides1200L and 1200R. Particularly, in the case of a glasses-type headmounted display, the angle of convergence of left and right imagesvaries due to such a phenomenon. As a result, a mismatch occurs in thespatial distance to virtual images adjusted in advance, causing theobserver to feel fatigue when observing the images. Specifically, whenthe spatial position at which the screen centers of left and rightvirtual images adjusted in advance intersect with each other is a pointC as shown at the right of FIG. 14, with the deformation of the frontpart 1010 a of the frame 1010, the spatial position as the point ofintersection of the screen centers of left and right virtual imagesshifts to a point D, resulting in an increase in the angle ofconvergence.

One approach to overcome the above issue is to enhance the stiffness ofthe front part 1010 a. However, such an approach leads to an increase inthe cross-sectional area of the frame 1010 and a necessity for using amaterial with a high Young's modulus, which can cause an increase in theweight of the frame 1010, deterioration in design, and an increase incosts.

Further, when there are flaws or dirt on a total reflection plane of thelight guides 1200L and 1200R, a loss or deviation of orientation appearspartially in guiding of display image light beams, and qualitydegradation occurs such as darkening of an image to be observed orlowering of resolution.

In light of the foregoing, it is desirable to provide a head mounteddisplay which displays images with high quality and design by minimizingthe effect of deformation of a frame occurring when worn on the head ofan observer on the relative positional relationship between an imageobtained by an optical module and the pupils of the observer.

According to an embodiment of the present invention, there is provided ahead mounted display which includes a glasses-type frame to be worn on ahead of an observer; two optical modules including two image creationdevices, and two light guides having two light guide plates coupledone-to-one with the two image creation devices and placed closer to acenter of a face of the observer than the image creation devices are asa whole, that guide light beams output from the image creation devicesand output the light beams toward pupils of the observer; and an opticalplate supporting the two light guides, wherein the optical plate isattached to a center part of the frame.

As described above, if the two image creation devices are supported bythe entire frame as shown in FIG. 14, the temples 1015 flex outward inthe direction of the arrow A, and the front part 1010 a of the frame1010 is deformed in the direction of the arrow B. Due to thedeformation, despite of pre-adjustment of the spatial position at whichthe screen centers of left and right virtual images intersect with eachother to the point C, the actual spatial position is shifted to thepoint D, resulting in an increase in the angle of convergence andlowering the quality of images.

However, according to the above configuration, the optical plate isattached to the center part of the frame in the state of supporting thetwo light guide plates coupled to the two image creation devices. Thetwo image creation devices are coupled one-to-one with the two lightguide plates which are placed closer to the center of an observer's facethan the image creation devices are as a whole. Therefore, the imagecreation devices are arranged symmetrically outside the face of anobserver when worn. The two image creation devices are coupled to thecenter part of the frame through the optical plate supporting the twolight guide plates. Thus, the image creation devices placed at both endsof the two light guide plates are supported only at the center part ofthe frame.

According to this, the two image creation devices are not supported bythe entire frame, thereby, flexure of the frame does not affect theposition of the light guide plates. Thus, the light waveguide is thusnot deviated. Thereby, it is possible to prevent deviation of theposition of image created by image creation devices of the left side andthe position of image created by image creation devices of the rightside. It is thereby possible to prevent change in the angle ofconvergence. This allows a user to view high quality images comfortablywithout providing a feeling of strangeness. According to the abovedescription, it is possible to provide a head mounted display whichdisplays images with high quality and design by minimizing the effect ofdeformation of a frame occurring when worn on the head of an observer onthe relative positional relationship between an image obtained by anoptical module and the pupils of the observer.

The optical plate may be fixed to the center part of the frame using aframe attachment member.

A center part of the optical plate may be reinforced by a joint memberincluding a reinforcing member and an adhesive bond.

The optical plate may be placed to cover surfaces of the two light guideplates.

The optical plate may be bonded to the two light guide plates by anadhesive bond containing a spacer.

The optical plate may be a flat transparent glass plate.

The optical plate may be coupled to respective rims of the two lightguide plates using a rail.

The two light guides may guide light beams respectively output from thetwo image creation devices by repeating total reflection respectively inthe two light guide plates, and

the optical plate may be bonded to total reflection planes of the twolight guide plates.

A center part of the frame may be thicker than an outside part.

Holographic optical elements may be respectively placed on an input sideand on an output side of each of the two light guide plates in the twolight guides.

The two light guide plates may have a mirror internally on an input sideand a half minor film on an output side.

According to the embodiments of the present invention described above,it is possible to provide a head mounted display which displays imageswith high quality and design by minimizing the effect of deformation ofa frame occurring when worn on the head of an observer on the relativepositional relationship between an image obtained by an optical moduleand the pupils of the observer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall structural view of a head mounted display accordingto a first embodiment of the present invention;

FIG. 2 is a perspective view (front side) of the head mounted displayaccording to the first embodiment;

FIG. 3 is a perspective view (rear side) of the head mounted displayaccording to the first embodiment;

FIG. 4 is a view to explain an image display device and a light guide ofthe head mounted display according to the first embodiment;

FIG. 5 is an overall structural view of a head mounted display accordingto a second embodiment of the present invention;

FIG. 6 is a view to explain an image display device and a light guide ofthe head mounted display according to the second embodiment;

FIG. 7 is a front view of the head mounted display according to thefirst embodiment;

FIG. 8 is a plan view of the head mounted display according to the firstembodiment;

FIG. 9 is a bottom view of the head mounted display according to thefirst embodiment;

FIG. 10 is a right side view of the head mounted display according tothe first embodiment;

FIG. 11 is a left side view of the head mounted display according to thefirst embodiment;

FIG. 12 is a rear view of the head mounted display according to thefirst embodiment;

FIG. 13 is a perspective view of the head mounted display according tothe first embodiment; and

FIG. 14 is a view showing an image display device according to relatedart attached to a glasses frame.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

Embodiments of the present invention will be described in the followingorder.

First Embodiment [Overall Structure of Head Mounted Display] [SupportingMethod] [Structure and Operation of Optical Module] Second Embodiment[Overall Structure of Head Mounted Display] [Structure and Operation ofOptical Module] First Embodiment [Overall Structure of Head MountedDisplay]

A head mounted display according to a first embodiment of the presentinvention is described hereinafter with reference to FIG. 1 as aconceptual illustration. At the bottom of FIG. 1 is a front view, and atthe top is a plan view. A head mounted display 10 according to theembodiment includes a frame 100, optical modules 200L and 200R, anoptical plate 300, a joint member 400, and a nose pad 500.

The frame 100 is a glasses-type frame to be worn on the head of anobserver. The frame 100 is composed of a front part 100 a placed at thefront of an observer and two temples 100 b rotatably attached to bothends of the front part 100 a through a hinge 100 c. The temples 100 bare foldable toward the front part 100 a with the hinge 100 c as asupporting point.

The frame 100 according to the embodiment substantially has the samestructure as normal glasses except that it does not have a rim. Thematerial of the frame 100 is the same as the material of normal glasses,such as metal, alloy, plastic, or a combination or those.

As the temples 100 b, a plurality of types such as for child use and foradult use are prepared to be replaceable. For example, the temples 100 bfor child use have a shape in which the angle is inclined inward withrespect to the front part 100 a compared to the temples 100 b for adultuse. This offers a better fit for children. Further, the temples 100 bof a plurality of types having different shapes can be replaced with oneanother in order to alter the vertical angle with respect to the frontpart 100 a. For example, the angle of sight of an observer differsbetween the first floor and the second floor of a theatre. Therefore,the temples 100 b with different vertical angles are attachedrespectively in the first floor and the second floor. The position of acaption displayed on the head mounted display 10 can be thereby variedbetween the first floor and the second floor.

The optical modules 200L and 200R create virtual images for the left eyeand the right eye and output the virtual images to the respective eyes.The optical module 200L includes an image creation device 210L and alight guide 230L having a light guide plate 220L. The image creationdevice 210L and the light guide plate 220L are joined by an adhesive orthe like, so that the position of the image creation device 210L isfixed relative to the light guide plate 220L.

Likewise, the optical module 200R includes an image creation device 210Rand a light guide 230R having a light guide plate 220R. The imagecreation device 210R and the light guide plate 220R are joined by anadhesive or the like, so that the position of the image creation device210R is fixed relative to the light guide plate 220R. In this manner,the image creation devices 210L and 210R are coupled one-to-one with thelight guide plates 220L and 220R which are placed closer to the centerof an observer's face than the image creation devices 210L and 210R areas a whole.

The light guides 230L and 230R input light beams output from the imagecreation devices 210L and 210R to the light guide plates 220L and 220R,respectively, guide the light beams by repeating total reflection insidethe light guide plates 220L and 220R, and then output them toward thepupils of the observer. A specific structure and operation of theoptical modules 200L and 200R including the light guides are describedlater.

The optical plate 300 is a flat transparent glass plate and made oftempered glass. Although the optical plate 300 is a flat plate in thisembodiment, it is not necessarily a flat plate as long as the lightguide plates 220L and 220R can be attached thereto. The optical plate300 supports the two light guides 230L and 230R. Specifically, the rearsurface of the optical plate 300 and the front surfaces of the lightguide plates 220L and 220R are bonded together in the periphery part ofthe light guide plates 220L and 220R by using an adhesive containingbead spacers with a diameter of about 30 μm, which are not shown. Theoptical plate 300 thereby supports the two light guide plates 220L and220R with a small airspace maintained between the optical plate 300 andthe light guide plates 220L and 220R. Because the glass surface of thetwo light guide plates 220L and 220R needs to act as a total internalreflection plane, the glass surface should be the airspace.

The joint member 400 is attached to the center (which corresponds to thebridge of normal glasses) of the front part 100 a located between thetwo pupils of an observer. Specifically, the optical plate 300 isattached to the center of the front part 100 a through the joint member400. The joint member 400 also has a role of reinforcing the center partof the optical plate 300. Specifically, the joint member 400 has a metalplate as a reinforcing member and an adhesive bond, and the metal plateand the center part of the optical plate 300 are bonded together by theadhesive bond.

As described above, the joint member 400 enhances the stiffness of theoptical plate 300 and further makes the optical plate 300 attached tothe center part of the frame 100 located between the two pupils of anobserver. The optical plate 300 may be attached to the frame 100 with ascrew, for example. The optical plate 300 is fixed to the center part ofthe frame 100 using a frame attachment member 450. The joint member 400and the frame attachment member 450 form an integrated stay.

The nose pad 500 is attached to the center of the front part 100 a. Tobe more specific, the nose pad 500 is attached to the joint member 400.

Not that, in this embodiment, a cover glass 600 that protects the lightguide plates 220L and 220R is mounted on the opposite side of theoptical plate 300 with the light guide plates 220L and 220R interposedtherebetween, which is on the backside of the light guide plates 220Land 220R. However, the cover glass 600 is not an essential element forthe head mounted display 10 according to the embodiment, and it may beeliminated.

In one image creation device, a line 700 connected to a PC (PersonalComputer), for example, is connected, so that image data is sent to theimage creation device 210R from the PC. One image creation device andthe other image creation device are connected by flexible wiring 750running on the top surface of the optical plate 300, so that image datais sent also to the other image creation device from the PC. Note thatthe PC and the two image creation devices 210L and 210R may performwireless data communication.

[Supporting Method]

The glasses-type head mounted display 10 according to the embodiment hasa structure in which the two optical modules 200L and 200R are supportedonly at the center part of the frame 100 through the optical plate 300.Hereinafter, a supporting method of the head mounted display isdescribed in detail with reference to FIGS. 2 and 3. FIG. 2 is aperspective view of the head mounted display according to the embodimentwhen viewed from the front side. FIG. 3 is a perspective view of thehead mounted display according to the embodiment when viewed from therear side.

In FIGS. 2 and 3, the optical plate 300, the light guide plates 220L and220R and the cover glass 600 are integrated together to form a glassespart. Referring to FIG. 2, in the front part 100 a of the frame 100, acenter part P to which the optical plate 300 is attached is thicker thanan outside part Q. When an observer wears the head mounted display 10 onthe head, the observer generally wears it by opening the both ends ofthe frame 100. At this time, stress is applied most heavily to thecenter of the frame 100. Thus, the center part P of the frame 100 has alarge thickness to enhance the breaking strength. However, if the entireframe is thick, the head mounted display 10 increases in weight, whichmakes it difficult to be worn and less easy to use. Therefore, theoutside part Q of the frame 100 has a smaller thickness than the centerpart P.

Because the head mounted display 10 has a contoured recess correspondingto the position of the nose of an observer, the optical plate 300 issubject to distortion near the contoured recess, which causes a decreasein breaking strength. Therefore, a rail 850 is attached to the contouredrecess of the optical plate 300 so as to reinforce the center part ofthe head mounted display 10.

Further, referring to FIG. 3, the optical plate 300 is coupled to therespective rims of the two light guide plates 220L and 220R bonded tothe rear surface of the optical plate 300 using the rail 850, and thecover glass 600. Further, the optical plate 300 is reinforced by a rail800 at its outer edges at both ends, and coupled to the respective rimsof the two light guide plates 220L and 220R and the cover glass 600.

As described above, the joint member 400 reinforces the optical plate300 at the center of the optical plate 300. Specifically, the jointmember 400 has a rectangular metal plate 400 a to serve as a reinforcingmember and an adhesive bond, and the metal plate 400 a and the centerpart of the optical plate 300 are bonded together by the adhesive bond.The shape of the joint member 400 is arbitrary, and it may have a barshape, a narrow plate shape or the like, for example. The material ofthe joint member 400 is preferably a metal such as aluminum, magnesium,stainless steel, titanium or glass-fiber carbon or an alloy of thosemetals, plastic, or a combination of those materials. The nose pad 500is attached to the joint member 400. The joint member 400 is joined tothe frame attachment member 450 and attached to the front part 100 a ofthe frame 100.

As described above, the head mounted display 10 according to theembodiment has a structure that supports the two optical modules 200Land 200R only at the center part of the frame 100 through the opticalplate 300, in addition that it is originally structurally weak at thecenter part with the presence of the contoured recess for the nose.Therefore, the glass is likely to be deformed at the center of theoptical plate 300, and stress is concentrated on the center part. Inlight of this, the breaking strength is enhanced by use of the jointmember 400 with the metal plate 400 a attached to the optical plate 300,the rail 850 and so on.

In addition, in order to increase the positioning accuracy of the twooptical modules 200L and 200R and clearly display desired images, it isdesigned to enhance the synthesis, which is elastic modulus (Young'smodulus), of the center part. For example, in order to increase thesynthesis at the center part of the cover glass 600, it is preferred tochange the material of the center part of the cover glass 600 to the onewith high synthesis, mix a material with high synthesis only at thecenter part of the cover glass 600, or form the center part of the coverglass 600 to be thicker than the other part.

[Structure and Operation of Optical Module]

The structure and the operation of the optical modules 200L and 200Raccording to the embodiment are described hereinafter with reference toFIG. 4. FIG. 4 is a conceptual diagram of the optical module 200L. Theoptical module 200R is placed symmetrically with the optical module 200Land structurally identical to the optical module 200L, and therefore itis not redundantly described herein.

The optical module 200L includes the image creation device 210L and thelight guide 230L. The image creation device 210L includes an imageformation unit 211 and a collimator optical system 212. The imageformation unit 211 and the collimator optical system 212 are housed in ahousing 213 (which is indicated by alternate long and short dashedlines). The housing 213 has an opening, which is not shown, and light isoutput from the collimator optical system 212 through the opening. Thehousing 213 is joined to the light guide 230L.

The image formation unit 211 has a plurality of pixels arranged intwo-dimensional matrix. The collimator optical system 212 converts lightoutput from the pixels of the image formation unit 211 into parallellight. The parallel light from the collimator optical system 212 isinput to the light guide plate 220L, guided therethrough and then outputfrom the light guide plate 220L.

The image formation unit 211 includes a light source 211 a, a liquidcrystal display device (LCD) 211 b, and a polarizing beam splitter 211c. The liquid crystal display device (LCD) 211 b and the polarizing beamsplitter 211 c form a reflection type spatial light modulator. Theliquid crystal display device (LCD) 211 b is a LCOS (Liquid Crystal onSilicon) as a light valve. The polarizing beam splitter 211 c reflects apart of the light emitted from the light source 211 a and guides thereflected light to the liquid crystal display device 211 b, andtransmits a part of the light emitted from the light source 211 a andguides the transmitted light to the collimator optical system 212.

The liquid crystal display device 211 b has a plurality of pixelsarranged in two-dimensional matrix. The polarizing beam splitter 211 chas a known structure and configuration. Non-polarized light emittedfrom the light source 211 a encounters the polarizing beam splitter 211c. At this time, p-polarized component of the light passes through thepolarizing beam splitter 211 c and exits to the outside of the system.On the other hand, s-polarized component of the light is reflected bythe polarizing beam splitter 211 c, input to the liquid crystal displaydevice 211 b, reflected inside the liquid crystal display device 211 b,and output from the liquid crystal display device 211 b.

Out of the light output from the liquid crystal display device 211 b,light output from a pixel for displaying “white” contains much of thep-polarized component, and light output from a pixel for displaying“black” contains much of the s-polarized component. Accordingly, out ofthe light output from the liquid crystal display device 211 b andencountering the polarizing beam splitter 211 c, the p-polarizedcomponent passes through the polarizing beam splitter 211 c and isguided to the collimator optical system 212. On the other hand, thes-polarized component is reflected by the polarizing beam splitter 211 cback to the light source 211 a.

The liquid crystal display device 211 b has 320×240 pixels arranged intwo-dimensional matrix (the number of liquid crystal cells is threetimes the number of pixels), for example. The collimator optical system212 is a convex lens, for example, and the liquid crystal display device211 b is placed at the position of a focal length in the collimatoroptical system 212 to create parallel light. Further, one pixel iscomposed of a red light emitting sub-pixel that emits red, a green lightemitting sub-pixel that emits green, and a blue light emitting sub-pixelthat emits blue.

The light guide 230L includes the light guide plate 220L, a firstpolarizer 240, and a second polarizer 250. The input light propagatesthrough the light guide plate 220L by repeating total internalreflection and is then output from the light guide plate 220L.

The first polarizer 240 reflects the light input to the light guideplate 220L so that the light is totally reflected inside the light guideplate 220L.

The first polarizer 240 is made of a metal including aluminum or analloy, for example, and composed of a light reflection film (a type ofminor) that reflects light input to the light guide plate 220L or adiffraction grating (e.g. holographic diffraction grating film) thatdiffracts light input to the light guide plate 220L.

The second polarizer 250 transmits and reflects the light havingpropagated by total reflection through the light guide plate 220L aplurality of times. The second polarizer 250 is composed of a lightreflection multilayer film having a multilayer laminated structure, forexample, and outputs the light as a plurality of light beams from thelight guide plate 220L. In this structure, a mirror is placed internallyon the input side, a half-minor film is placed on the output side, thefirst polarizer 240 functions as a reflection minor, and the secondpolarizer 250 functions as a semitransparent mirror.

The second polarizer 250 may be composed of a multi-stack structure withmultiple dielectric film stacks, a half mirror, a polarizing beamsplitter, a holographic diffraction grating film or the like. Thedielectric film stack is made of a TiO₂ film as a high dielectricconstant material and a SiO₂ film as a low dielectric constant material.The multi-stack structure with multiple dielectric film stacks isdisclosed in Published Japanese Translation No. 2005-521099 of PCTInternational Publication. Although six-layer dielectric film stacks areillustrated in FIG. 4, it is not limited thereto. A thin piece made ofthe same material as the material of the light guide plate 220L isinterposed between the dielectric film stack and the dielectric filmstack.

Note that, in the first polarizer 240, parallel light input to the lightguide plate 220L is reflected (or diffracted) in such a way that theparallel light input to the light guide plate 220L is totally reflectedinside the light guide plate 220L. On the other hand, in the secondpolarizer 250, the parallel light having propagated by total reflectionthrough the light guide plate 220L is reflected (or diffracted) aplurality of times and output from the light guide plate 220L in theform of parallel light.

The first polarizer 240 may be formed by carving out a portion 240 a forthe first polarizer 240 of the light guide plate 220L to make a slope toform the first polarizer 240 in the light guide plate 220L,vacuum-depositing a light reflection film on the slope, and then bondingthe carved portion 240 a of the light guide plate 220L onto the firstpolarizer 240. Further, the second polarizer 250 may be formed byproducing a multilayer laminated structure composed of multiplelamination of the same material (e.g. glass) as the material of thelight guide plate 220L and the dielectric film stack (which may beformed by vacuum deposition, for example), forming a slope by carvingout a portion S for the second polarizer 250 of the light guide plate220L, bonding the multilayer laminated structure onto the slope, andthen completing the outer shape by grinding or the like. The light guide230L in which the first polarizer 240 and the second polarizer 250 areplaced inside the light guide plate 220L is thereby formed.

The light guide plate 220L has two parallel planes (a first plane F anda second plane R) which lie in parallel with the axis line (Y direction)of the light guide plate. The first plane F and the second plane R areopposed to each other. When the plane of the light guide plate 220L towhich light is input is referred to as a light guide plate inputsurface, and the plane of the light guide plate 220L from which light isoutput is referred to as a light guide plate output surface, the lightguide plate input surface and the light guide plate output surface maybe formed by the first plane F, or the light guide plate input surfaceand the light guide plate output surface may be formed by the secondplane R. In this example, parallel light is input from the first plane Fwhich corresponds to the light input surface, and propagates internallyby total reflection, and then output from the second plane R whichcorresponds to the light output surface.

The material of the light guide plate 220L may be glass includingoptical glass such as quartz glass or BK7, a plastic material (e.g.PMMA, polycarbonate resin, acrylic resin, amorphous polypropylene resin,styrene resin containing AS resin etc.) or the like. The shape of thelight guide plate 220L is not limited to a flat plate, and it may have acurved shape.

In the above structure, the light guides 230L and 230R of the headmounted display 10 guide light beams respectively output from the imagecreation devices 210L and 210R by repeating total reflection through thelight guide plates 220L and 220R. The optical plate 300 is bonded to thetotal reflection plane of the light guide plates 220L and 220R. Becausethe light beams propagating through the light guide plates 220L and 220Rare guided with total reflection, when there are flaws or dirt on thelight guide plates 220L and 220R, the guiding of light stops or a lightpath is deviated. Therefore, the optical plate 300 is an essentialelement for protecting the light guide plates 220L and 220R andpreventing flaws or dirt from being present on the surfaces of the lightguide plates 220L and 220R so as to ensure the total reflection in thelight guide plates 220L and 220R. Likewise, the airspace is placedbetween the optical plate 300 and the light guide plates 220L and 220Ris for the purpose of ensuring the total reflection of light by theairspace.

FIGS. 7 to 13 are illustrations of a more specific shape of the headmounted display 10 according to the embodiment. FIG. 7 is a front viewof the head mounted display 10, FIG. 8 is a plan view, FIG. 9 is abottom view, FIG. 10 is a right side view, FIG. 11 is a left side view,FIG. 12 is a rear view, and FIG. 13 is a perspective view. The headmounted display 10 shown in FIGS. 7 to 13 may be also regarded ascreation of design. As the article to which the design is applied, itcorresponds to “data display device” as classification of article equalto the classification of article in Appendix I, Regulations under theDesign law.

As the explanation of the article to which the design is applied, thefollowing explanation may be provided. Specifically, the article towhich the design is applied is a head mounted display which includes aglasses-type frame to be worn on the head of an observer, an opticalmodule, and an optical plate.

Further, the article to which the design is applied may have anadjustable nose pad which is vertically slidable. This enablescompatibility with both those wearing and not wearing glasses.Specifically, by adjusting the nose pad up or down, the article does notonly allows an observer who is not wearing glasses to wear the headmounted display 10 but also allows an observer who is wearing glasses towear the head mounted display 10 on top of the glasses.

The head mounted display 10 according to the embodiment is descriedabove. If the two optical modules 200L and 200R are supported by theentire frame as shown in FIG. 14, the temples 1015 flex outward in thedirection of the arrow A, and the front part 1010 a of the frame 1010 isdeformed in the direction of the arrow B. Due to the deformation,despite of pre-adjustment of the spatial position at which the screencenters of left and right virtual images intersect with each other tothe point C, the actual spatial position is shifted to the point D,resulting in an increase in the angle of convergence.

However, in the head mounted display 10 according to the embodiment, theoptical plate 300 is attached to the center part of the frame 100 in thestate of supporting the two light guide plates 220L and 220R coupled tothe two image creation devices 210L and 210R. The two image creationdevices 210L and 210R are coupled one-to-one with the two light guideplates 220L and 220R which are placed closer to the center of anobserver's face than the image creation devices 210L and 210R are as awhole. Therefore, the image creation devices 210L and 210R are arrangedsymmetrically outside the face of an observer when worn. The two imagecreation devices 210L and 210R are coupled to the center part P of theframe 100 through the optical plate 300 supporting the two light guideplates 220L and 220R. Thus, the image creation devices 210L and 210Rplaced at both ends of the two light guide plates 220L and 220R aresupported only at the center part P of the frame 100.

In this structure, the optical modules 200L and 200R are supported atthe center part so as to minimize flexure of the frame 100 and, evenwhen flexure occurs, to prevent a difference in flexure between left andright from causing a significant effect. Accordingly, the flexure of theframe 100 when worn by an observer does not affect the position of thelight guide plates 220L and 220R. The light waveguide is thus notdeviated. Thus, even when the temples 100 b flex outward andconsequently the frame is deformed when an observer wears the frame 100on the head, the deformation of the frame does not cause displacement(change in position) of the light guides 230L and 230R, or causes onlyslight displacement if any. It is thereby possible to reliably prevent achange in the angle of convergence of left and right images. This allowsa user to view images comfortably. Further, because there is no need toenhance the stiffness of the front part 100 a of the frame 100, it ispossible to suppress the frame weight from increasing without anincrease in costs and thereby provide the head mounted display 10 withhigh level of design.

Second Embodiment [Overall Structure of Head Mounted Display]

An overall structure of a head mounted display according to a secondembodiment of the present invention is described hereinafter. The secondembodiment is an alternative example of the first embodiment. Referringto FIG. 5, the head mounted display 10 according to the secondembodiment has a structure in which first polarizers 280L and 280R andsecond polarizers 285L and 285R are mounted on the surfaces of the lightguide plates 220L and 220R, which is different from the structure of thehead mounted display 10 according to the first embodiment in which thefirst polarizer 240 and the second polarizer 250 are formed in carvedportions of the light guide plates 220L and 220R. The head mounteddisplay 10 according to the second embodiment is described hereinaftermainly about such a difference.

As shown in the plan view of the head mounted display 10 at the top ofFIG. 5, on the surfaces of the light guide plates 220L and 220R on theoptical plate side, film-like holographic optical elements are attachedas the first polarizers 280L and 280R and the second polarizers 285L and285R, respectively on the input side and the output side of each lightguide plate.

In this embodiment, the cover glass 600 is not provided on the rearsurfaces of the light guide plates 220L and 220R. The head mounteddisplay 10 according to the second embodiment may be provided with ornot provided with the cover glass 600. On the other hand, the opticalplate 300, particularly, is an essential element in the secondembodiment. This is because, in this embodiment, the holograms (films)attached on the surfaces of the light guide plates 220L and 220R arevery weak, and it is therefore necessary to protect them with theoptical plate 300.

The first polarizers 280L and 280R diffract the light input to the lightguide plates 220L and 220R, and the second polarizers 285L and 285Rdiffract the light having propagated by total reflection through thelight guide plates 220L and 220R a plurality of times. The firstpolarizers 280L and 280R and the second polarizers 285L and 285R arediffraction grating elements, or reflection type diffraction gratingelements to be specific, or reflection type volume holographicdiffraction gratings to be more specific. In the following description,the first polarizers 280L and 280R being the reflection type volumeholographic diffraction gratings are referred to as first diffractiongrating members 2801 and 280 r, and the second polarizers 285L and 285Rbeing the reflection type volume holographic diffraction gratings arereferred to as second diffraction grating members 2851 and 285 r,respectively, for the sake of convenience.

In this embodiment, in order that the first diffraction grating members2801 and 280 r and the second diffraction grating members 2851 and 285 rcorrespond to diffraction/reflection of P types of light having Pdifferent types (specifically, P=3; three types including red, green andblue) of wavelength bands (or wavelengths), P number of diffractiongrating layers made of reflection type volume holographic diffractiongratings are laminated.

The material of the first diffraction grating members and the seconddiffraction grating members may be photopolymer. The constructionmaterial and the basic structure of the first diffraction gratingmembers and the second diffraction grating members which are reflectiontype volume holographic diffraction gratings are the same as theconstruction material and the structure of the existing reflection typevolume holographic diffraction grating. The reflection type volumeholographic diffraction grating means a holographic diffraction gratingwhich diffracts or reflects only the +1st order diffracted light beam.The diffraction grating members have an interference pattern from theinside to the surface, and a method of forming the interference patternmay be the same as the existing formation method. Specifically, theinterference pattern may be formed by applying object light to a member(e.g. phoropolymer material) constituting the diffraction grating memberfrom a first given direction on one side and, simultaneously applyingreference light to the member constituting the diffraction gratingmember from a second given direction on the other side, and thenrecording an interference pattern formed by the object light and thereference light inside the member constituting the diffraction gratingmember. By appropriately selecting the first given direction, the secondgiven direction, and wavelengths of the object light and the referencelight, a desired pitch of the interference pattern on the surface of thediffraction grating member and a desired slant angle of the interferencepattern can be obtained. The slant angle of the interference patternmeans an angle between the surface of the diffraction grating member (ordiffraction grating layer) and interference light.

In the case of forming the first diffraction grating members and thesecond diffraction grating members using a laminated structure of Pnumber of diffraction grating layers made of the reflection type volumeholographic diffraction grating, the lamination of diffraction gratinglayers may be formed by creating P number of diffraction grating layersseparately and then laminating (bonding) the P number of diffractiongrating layers using UV curable adhesive, for example. Further, the Pnumber of diffraction grating layers may be created by creating a singlediffraction grating layer using an adhesive photopolymer material andthen creating diffraction grating layers by attaching an adhesivephotopolymer material thereon one by one.

Each of the first diffraction grating members 2801 and 280 r and thesecond diffraction grating members 2851 and 285 r may have a structurein which a diffraction grating layer that diffracts or reflects redlight, a diffraction grating layer that diffracts or reflects greenlight, and a diffraction grating layer that diffracts or reflects bluelight are laminated.

[Structure and Operation of Optical Module]

The structure and operation of the optical module 200L, 200R accordingto the embodiment are described hereinafter with reference to FIG. 6.FIG. 6 is a conceptual diagram of the optical module 200L. In thisembodiment also, the optical module 200R is placed symmetrically withthe optical module 200L and structurally identical in structure to theoptical module 200L, and therefore redundant explanation is omitted, andthe structure and operation of only the optical module 200L aredescribed.

In FIG. 6, each of the first diffraction grating member 2801 and thesecond diffraction grating member 2851 is illustrated as a single layer.The interference pattern corresponding to one type of wavelength band isformed in each diffraction grating layer. Further, in order tocorrespond to diffraction/reflection of P types of light beams having Pdifferent types of wavelength bands, P types of interference patternsmay be formed on the first diffraction grating member and the seconddiffraction grating member made of a single diffraction grating layer.Further, the angle of view may be divided equally among three, forexample, so that the first diffraction grating member and the seconddiffraction grating member have a laminated structure of diffractiongrating layers corresponding to the respective divided angles of view.Such a structure enables an increase in diffraction efficiency, anincrease in diffraction angle range, and optimization of the angle ofdiffraction when the light beam having each wavelength band (orwavelength) is diffracted or reflected by the first diffraction gratingmember 2801 and the second diffraction grating member 2851.

FIG. 6 further shows a schematic enlarged partial cross-sectional viewof the reflection type volume holographic diffraction grating at itsupper right (b). An interference pattern having a slant angle φ isformed in the reflection type volume holographic diffraction grating.The slant angle φ is an angle between the surface of the reflection typevolume holographic diffraction grating and the interference pattern. Theinterference pattern is formed from the inside to the surface of thereflection type volume holographic diffraction grating. The interferencepattern satisfies the Bragg condition. The Bragg condition is acondition that satisfies the following equation (1).

m·λ=2·d·sin(Θ)   Equation (1)

In the equation (1), m is a positive integer, λ is a wavelength, d is apitch of a lattice plane (interval of a virtual plane including aninterference pattern in the direction of the normal), and Θ is asupplementary angle of the angle incident on the interference pattern.Further, the relationship of the supplementary angle Θ, the slant angleφ, and the incidence angle ψ when light enters the diffraction gratingmember at the incidence angle ψ is as represented by the followingequation (2).

Θ=90°−(φ+ψ)   Equation (2)

The first diffraction grating member 2801 is a film as described above,which is attached to the second plane R of the light guide plate 220L.The second diffraction grating member 2851 is also a film, which isattached to the first plane F of the light guide plate 220L. Parallellight input to the light guide plate 220L from the second plane Rpropagates by total reflection through the light guide plate 220L, isdiffracted or reflected a plurality of times, and then output asparallel light from the second plane R of the light guide plate 220L.

In the light guide plate 220L also, three colors, red, green and blue,of parallel light propagate by total reflection therethrough and arethen output. Because the light guide plate 220L is thin and an opticalpath running inside the light guide plate 220L is long, the number oftimes of total reflection until reaching the second diffraction gratingmember 2851 differs depending on the angle of view. Specifically, thenumber of times of reflection of the parallel light which is input tothe light guide plate 220L at an angle in the direction getting closerto the second diffraction grating member 2851 is smaller than the numberof times of reflection of the parallel light which is input to the lightguide plate 220L at an angle in the direction getting away from thesecond diffraction grating member 2851. This is because the angle oflight propagating through the light guide plate 220L with respect to thenormal to the light guide plate 220L upon encountering the inner surfaceof the light guide plate 220L is smaller for the parallel light which isdiffracted or reflected on the first diffraction grating member 2801 andinput to the light guide plate 220L at an angle in the direction gettingcloser to the second diffraction grating member 2851 than for theparallel light input to the light guide plate 220L at an angle in theopposite direction. Further, the shape of the interference patternformed inside the second diffraction grating member 2851 and the shapeof the interference pattern formed inside the first diffraction gratingmember 2801 are symmetrical with respect to a virtual planeperpendicular to the axis line of the light guide plate 220L.

The head mounted display 10 according to this embodiment also has theoptical plate 300 which joins the two light guide plates 220L and 220R.The joint member 400 made of aluminum is attached to the center of theoptical plate 300. The joint member 400 is placed for the purpose ofenhancing the stiffness of the optical plate 300. The optical plate 300and the optical modules 200L and 200R may be attached to the center partof the frame 100 located between two pupils of an observer by the jointmember 400 and a frame attachment member, which is not shown. Theoptical plate 300 is attached to the frame 100 using a screw or anadhesive, for example.

The image creation devices 210L and 210R of the optical modules 200L and200R are respectively located outside the pupils of an observer. The twolight guide plates 220L and 220R and the optical plate 300 are bondedtogether in the peripheral part of the light guide plates 220L and 220Rwith bead spacers with a diameter of about 30 μm, which are not shown,interposed therebetween. This is because the glass surface of the twolight guide plates 220L and 220R needs to act as a total internalreflection plane, and the glass surface should be the airspace. It isthereby possible to protect the input side hologram (first diffractiongrating member 2801 and 280 r) and the output side hologram (seconddiffraction grating member 2851 and 285 r) attached on the surfaces ofthe light guide plates 220L and 220R.

The frame 100 is composed of the front part 100 a to be placed at thefront of an observer and the two temples 100 b rotatably attached toboth ends of the front part 100 a through a hinge 100 c. The opticalplate 300 is attached to the center of the front part 100 a locatedbetween two pupils of an observer by the joint member 400 made ofaluminum. The nose pad 500 is attached at the center of the front part100 a.

As mentioned above, the other basic structure of the head mounteddisplay 10 according to the second embodiment is the same as that of thehead mounted display 10 according to the first embodiment and thus notredundantly described.

As described above, in the structure of the head mounted display 10according to the second embodiment, like the head mounted display 10according to the first embodiment, even when the temples 100 b flexoutward and consequently the frame is deformed when an observer wearsthe frame on the head, the deformation of the frame does not causedisplacement (change in position) of the light guides, or causes onlyslight displacement if any. It is thereby possible to reliably prevent achange in the angle of convergence of left and right images. This allowsa user to view images comfortably. Further, because there is no need toenhance the stiffness of the front part 100 a of the frame 100, it ispossible to suppress the frame weight from increasing without anincrease in costs and thereby provide the head mounted display 10 withhigh level of design.

Although preferred embodiments of the present invention are described indetail above with reference to the appended drawings, the presentinvention is not limited thereto. It should be understood by thoseskilled in the art that various modifications, combinations,sub-combinations and alterations may occur depending on designrequirements and other factors insofar as they are within the scope ofthe appended claims or the equivalents thereof.

For example, the structure and configuration of the head mounted displaydescribed in each of the above embodiments are given by way ofillustration and may be varied as appropriate. As an example, a surfacerelief type hologram (cf. United States Patent No. 20040062505A1) may bedisposed on the light guide plate.

For the light guides 230L and 230R according to the second embodiment,the diffraction grating elements may be formed using transmissiondiffraction grating elements. Alternatively, either one of the firstpolarizer or the second polarizer may be formed using a reflectiondiffraction grating element, and the other one may be formed using atransmission diffraction grating element. Further, the diffractiongrating element may be a reflection type blazed diffraction gratingelement.

As an alternative example of the first and second embodiments, an activematrix image formation unit may be used which includes a semiconductorlight emitting element composed of light emitting panels arranged intwo-dimensional matrix and which displays images by controlling thelight emitting/non-emitting state of each of the semiconductor lightemitting element so as to allow direct viewing of the light emissionstate of the semiconductor light emitting element. In this case also,light output from the image formation unit is input to the light guideplates through the collimator optical system.

The image formation unit may perform image formation for color displaywhich controls the light emitting/non-emitting state of each of a redlight emitting element, a green light emitting element, and a blue lightemitting element. In this case also, light output from the imageformation unit is input to the light guide plates through the collimatoroptical system.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2010-087785 filedin the Japan Patent Office on Apr. 6, 2010, the entire content of whichis hereby incorporated by reference.

1. A head mounted display comprising: a glasses-type frame to be worn ona head of an observer; two optical modules including two image creationdevices, and two light guides having two light guide plates coupledone-to-one with the two image creation devices and placed closer to acenter of a face of the observer than the image creation devices are asa whole, that guide light beams output from the image creation devicesand output the light beams toward pupils of the observer; and an opticalplate supporting the two light guides, wherein the optical plate isattached to a center part of the frame.
 2. The head mounted displayaccording to claim 1, wherein the optical plate is fixed to the centerpart of the frame using a frame attachment member.
 3. The head mounteddisplay according to claim 1, wherein a center part of the optical plateis reinforced by a joint member including a reinforcing member and anadhesive bond.
 4. The head mounted display according to claim 1, whereinthe optical plate is placed to cover surfaces of the two light guideplates.
 5. The head mounted display according to claim 1, wherein theoptical plate is bonded to the two light guide plates by an adhesivebond containing a spacer.
 6. The head mounted display according to claim1, wherein the optical plate is a flat transparent glass plate.
 7. Thehead mounted display according to claim 1, wherein the optical plate iscoupled to respective rims of the two light guide plates using a rail.8. The head mounted display according to claim 1, wherein the two lightguides guide light beams respectively output from the two image creationdevices by repeating total reflection respectively in the two lightguide plates, and the optical plate is bonded to total reflection planesof the two light guide plates.
 9. The head mounted display according toclaim 1, wherein a center part of the frame is thicker than an outsidepart.
 10. The head mounted display according to claim 1, whereinholographic optical elements are respectively placed on an input sideand on an output side of each of the two light guide plates in the twolight guides.
 11. The head mounted display according to claim 1, whereinthe two light guide plates have a mirror internally on an input side anda half minor film on an output side.